In recent years, with the development of material technology, display panels that are bendable have become possible. A flexible display is a deformable and bendable display device made of flexible materials. A flexible display panel has many advantages such as low power consumption, direct viewability, bendability, deformability, and portability, and can be mounted on a curved surface and made into a wearable display. It is predicted that flexible display panels may become the mainstream of the display field in the future.
However, the luminance uniformity of the entire screen deteriorates with a gradually increasing screen size and an improved resolution of the display device, which has been a problem existing in various display devices comprising a flexible display panel.
A flexible display panel usually uses self-luminous devices as light-emitting elements, e.g., an organic light emitting diode (OLED for short). In a display device using OLED elements, the OLED elements are provided with a pixel circuit for dimming. FIG. 1 schematically shows a circuit diagram of a pixel circuit of an ordinary flexible display panel using OLED elements as light-emitting elements. The pixel circuit comprises two thin film transistors (TFT for short) 103 and 104, a capacitance element 105 and an OLED element 106. The source of the TFT 104 is connected to a power supply line 100 that provides a supply voltage VDD, and the drain thereof is connected to the anode of the OLED element 106. The capacitance element 105 is provided between the source and the gate of the TFT 104. The gate of TFT 103 is connected to a scan line 102, and the source thereof is connected to a data line 101 that provides a data voltage Vdata, and the drain thereof is connected to the gate of the TFT 104. When the TFT 103 is switched on by the level of the scan line 102, charges are accumulated from the capacitance element 105 to the gate of the TFT 104 such that the voltage of the gate equals the data voltage Vdata. Then, when the TFT 103 turns into an off state, owing to the charge retention effect of the capacitance element 105, the voltage between the gate and the source of the TFT 104 remains VDD-Vdata. Since the current I passing through the OLED element 106 depends on the voltage between the gate and the source of the TFT 104, and the current I passing through the OLED element 106 determines the luminance of pixels of the flexible display panel, in order to obtain luminance uniformity of the flexible display panel, it is desirable to keep the supply voltage VDD constant in an effective display region. However, a voltage drop will be caused on the power supply wiring from the power supply circuit to the pixel circuit, so the supply voltage applied to each pixel may be different. As can be seen, the voltage drop on the power supply wiring of the display panel is an important reason for the deterioration of the luminance uniformity of the entire screen, hence the voltage drop on the power supply wiring should be decreased as much as possible.
In order to reduce the influence of the voltage drop of the power supply wiring on the luminance uniformity of the display panel, a conventional solution usually designs a corresponding compensation circuit for pixels in each row or each column. Nevertheless, such an approach adds to the complexity of the control circuit of the display panel and is adverse for the accurate control of the display panel. Moreover, it also increases the volume of the display panel and augments the manufacture cost.